There is an ongoing effort to develop systems that are more energy-efficient. A large proportion (some estimates are as high as twenty-five percent) of the electricity generated in the United States each year goes to lighting, a large portion of which is general illumination (e.g., downlights, flood lights, spotlights and other general residential or commercial illumination products). Accordingly, there is an ongoing need to provide lighting that is more energy-efficient.
Solid state light emitters (e.g., light emitting diodes) are receiving much attention due to their energy efficiency. It is well known that incandescent light bulbs are very energy-inefficient light sources—about ninety percent of the electricity they consume is released as heat rather than light. Fluorescent light bulbs are more efficient than incandescent light bulbs (by a factor of about 10) but are still less efficient than solid state light emitters, such as light emitting diodes.
In addition, as compared to the normal lifetimes of solid state light emitters, e.g., light emitting diodes, incandescent light bulbs have relatively short lifetimes, i.e., typically about 750-1000 hours. In comparison, light emitting diodes, for example, have typical lifetimes between 50,000 and 70,000 hours. Fluorescent bulbs generally have lifetimes (e.g., 10,000-20,000 hours) that are longer than those of incandescent lights, but they typically provide less favorable color reproduction. The typical lifetime of conventional fixtures is about 20 years, corresponding to a light-producing device usage of at least about 44,000 hours (based on usage of 6 hours per day for 20 years). Where the light-producing device lifetime of the light emitter is less than the lifetime of the fixture, the need for periodic change-outs is presented. The impact of the need to replace light emitters is particularly pronounced where access is difficult (e.g., vaulted ceilings, bridges, high buildings, highway tunnels) and/or where change-out costs are extremely high.
There are a number of challenges presented with using light emitting diodes in lighting devices. In many cases, additional components are added to the lighting devices in order to address these challenges. Additional components tend to increase the weight of lighting devices, as well as the size of lighting devices. It would be desirable to provide a lighting device that comprises one or more solid state light emitters, in which such challenges are addressed and yet the lighting device is lightweight and/or can fit within the same or substantially the same space that is provided for comparable conventional lighting devices (e.g., lighting devices that include one or more incandescent light sources and/or one or more fluorescent light sources). The ability for the lighting device to be lightweight and/or to fit in a space that is similar to (or identical to) a space into which conventional devices can fit is important when retro-fitting a lighting device, as well when installing a lighting device in new construction (let alone when shipping it).
One such challenge results from the fact that the emission spectrum of any particular light emitting diode is typically concentrated around a single wavelength (as dictated by the light emitting diode's composition and structure), which is desirable for some applications, but not desirable for others, (e.g., for providing general illumination, such an emission spectrum generally does not provide light that appears white, and/or provides a very low CRI). As a result, in many cases (e.g., to make devices that emit light perceived as white or near-white, or to make devices that emit light that is not highly saturated) it is necessary to employ light sources (e.g., one or more solid state light emitters and optionally also one or more other types of light sources, e.g., additional light emitting diodes, luminescent materials, incandescent lights, etc.) that emit light of different colors. There are a variety of reasons that one or more solid state light emitters might cease emitting light and/or vary in their intensity of light emission, which can throw off the balance of color output and cause the lighting device to emit light that is perceived as being of a color that differs from the desired color of light output. As a result, in many of such devices, one challenge that necessitates the inclusion of additional components, is that there may be a desire to provide additional circuitry that can adjust the current supplied to respective solid state light emitters (and/or other light emitters) in order to maintain the balance of color output among the light emitters that emit light of different colors in order to achieve the desired color output. Another such challenge is that there may be a desire to mix the light of different colors emitted from the different solid state light emitters by providing additional structure to assist in such mixing.
One example of a reason that one or more solid state light emitters might vary in their intensity of light emission is temperature change (resulting, e.g., from change in ambient temperature and/or heating up of the solid state light emitters). Some types of solid state light emitters (e.g., solid state light emitters that emit light of different colors) experience differences in intensity of light emission (if supplied with the same current) at different temperatures, and frequently such changes in intensity occur to differing extents for emitters that emit light of different colors as temperature changes. For example, some light emitting diodes that emit red light have a very strong temperature dependence in at least some temperature ranges (e.g., AlInGaP light emitting diodes can reduce in optical output by ˜20% when heated up by ˜40 degrees C., that is, approximately −0.5% per degree C.; some blue light emitting InGaN+YAG:Ce light emitting diodes can reduce in optical output by about −0.15%/degree C.).
Another example of a reason that one or more solid state light emitters might vary in their intensity of light emission is aging. Some solid state light emitters (e.g., solid state light emitters that emit light of different colors) experience decreases in intensity of light emission (if supplied with the same current) as they age, and frequently such decreases in intensity occur at differing rates.
Another example of a reason that one or more solid state light emitters might vary in their intensity of light emission is damage to the solid state light emitter(s) and/or damage to circuitry that supplies current to the solid state light emitter(s).
Another challenge presented in making a lighting device with light emitting diodes, that often necessitates the inclusion of additional components, is that the performance of many solid state light emitters may be reduced when they are subjected to elevated temperatures. For example, many light emitting diode light sources have average operating lifetimes of decades as opposed to just months or 1-2 years for many incandescent bulbs, but some light emitting diodes' lifetimes can be significantly shortened if they are operated at elevated temperatures. A common manufacturer recommendation is that the junction temperature of a light emitting diode should not exceed 85 degrees C. if a long lifetime is desired. There may be a desire to counteract such problems, in many instances, by providing additional structure (or structures) to provide a desired degree of heat dissipation.
Another challenge presented in making a lighting device with light emitting diodes, that often necessitates the inclusion of additional components, arises from the relatively high light output from a relatively small area provided by solid state emitters. Such a concentration of light output may present challenges in providing solid state lighting systems for general illumination in that, in general, a large difference in brightness in a small area may be perceived as glare and may be distracting to occupants. In many instances, therefore, there is a desire to provide additional structure to assist in mixing the emitted light and/or creating the perception that the emitted light is output through a larger area.
Another challenge presented in making a lighting device with light emitting diodes, that often necessitates the inclusion of additional components, is that light emitting diodes are typically run most effectively on low voltage DC current, while line voltage typically is much higher voltage AC current. As a result, there is often a desire to provide circuitry that converts line voltage, e.g., from AC to DC and/or that reduces voltage.
In addition, in some circumstances, there is a desire either to retrofit or install a lighting device in a circuit that has a conventional dimmer. Some dimmers operate based on signals contained in the current supplied to the lighting device (for example, duty cycle of an AC signal, e.g., from a triac), for which additional circuitry is generally needed. An example of a lighting device that includes some or all of these various additional components, retrofits into many conventional recessed lighting housings and works with many conventional dimmers is the LR6 from Cree LED Lighting Solutions of Morrisville, N.C. The LR6 is a 6 inch recessed downlight that provides 650 delivered lumens of light, consumes only 12 watts of electrical power and has a CRI of 92. The LR6 weighs slightly less than 1 kg.
It would be desirable to be able to make lighting devices that include solid state light emitters in order to achieve high wall plug efficiency, while providing consistently good color quality, suitable brightness and good solid state light emitter lifetimes, in a lighting device that is of light weight (e.g., in comparison to other lighting devices that comprise solid state light emitters, for example, devices that comprise one or more solid state light emitters and that provide some or all of the features described herein).